Re: [PATCH V3 1/2] mm: avoid marking swap cached page as lazyfree
From: Michal Hocko <mhocko@kernel.org>
Date: 2017-09-26 20:23:30
Also in:
linux-mm
On Tue 26-09-17 10:26:25, Shaohua Li wrote:
From: Shaohua Li <redacted> MADV_FREE clears pte dirty bit and then marks the page lazyfree (clear SwapBacked). There is no lock to prevent the page is added to swap cache between these two steps by page reclaim. Page reclaim could add the page to swap cache and unmap the page. After page reclaim, the page is added back to lru. At that time, we probably start draining per-cpu pagevec and mark the page lazyfree. So the page could be in a state with SwapBacked cleared and PG_swapcache set. Next time there is a refault in the virtual address, do_swap_page can find the page from swap cache but the page has PageSwapCache false because SwapBacked isn't set, so do_swap_page will bail out and do nothing. The task will keep running into fault handler.
Thanks for the clarification in the changelog. It is much more clear now!
Reported-and-tested-by: Artem Savkov <redacted> Fix: 802a3a92ad7a(mm: reclaim MADV_FREE pages) Signed-off-by: Shaohua Li <redacted> Cc: stable@vger.kernel.org Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Hillf Danton <redacted> Cc: Minchan Kim <minchan@kernel.org> Cc: Hugh Dickins <hughd@google.com> Cc: Mel Gorman <redacted> Cc: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Rik van Riel <redacted>
Marking for stable as suggested by Johannes makes perfect sense to me. Acked-by: Michal Hocko <mhocko@suse.com>
quoted hunk ↗ jump to hunk
--- mm/swap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)diff --git a/mm/swap.c b/mm/swap.c index 9295ae9..a77d68f 100644 --- a/mm/swap.c +++ b/mm/swap.c@@ -575,7 +575,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec, void *arg) { if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) && - !PageUnevictable(page)) { + !PageSwapCache(page) && !PageUnevictable(page)) { bool active = PageActive(page); del_page_from_lru_list(page, lruvec,@@ -665,7 +665,7 @@ void deactivate_file_page(struct page *page) void mark_page_lazyfree(struct page *page) { if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) && - !PageUnevictable(page)) { + !PageSwapCache(page) && !PageUnevictable(page)) { struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs); get_page(page);-- 2.9.5
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